The present invention relates to high-resilience, flexible and semi-flexible, flame-resistant, polyether-based, polyurethane foams and formulations for preparing the same.
In recent years there has been a growing awareness of the need for greater resistance to combustion of seating and trim materials, particularly in applications where a number of people may be at risk at the one time, such as rail carriages, aircraft, buses, boats, public buildings and hospitals where large amounts of combustible materials are present. Polyvinyl chloride foams (PVC) have relatively good performance in fire, but their comfort and recovery properties are poor. Thin liner sheets of special neoprene (polychloroprene) have been used to protect polyurethane seat pads, but when the liner is cut as a result of vandalism, the degree of protection is reduced or eliminated. Since polyurethane is currently by far the most widely used cushioning material, continuing attempts have been made to improve its resistance to combustion, but so far the success achieved has been very limited. Research carried out in all developed countries has been based on the inclusion of a wide range of fire retardant materials in the urethane reaction mixture. However, when the proportion of fire retardant materials is increased beyond quite low levels, the result has been a severe falling off in properties such as compression set so that either the improvement in fire retardance has been minimal, or performance of the foam in service has been unacceptable.
It is the purpose of this invention to produce flexible or semi-flexible foams with very high levels of flame retardance yet with a combination of physical properties equal to the combination of physical properties in the best foams currently available. These foams can be moulded, cut to shape or laid down on a backing material, so affording protection against fire in depth.
Flexible and semi-flexible foams only are within the ambit of this invention. The term "flexible", as understood in the art, indicates the use of polyols the molecular weights of which are between 1000 and 10,000 but usually between 3000 and 6500, and the functionality of which is 2 to 3, reacted with isocyanates having a functonality of two or three, to form the foam. These foams have relatively low crosslink densities. The term "semi-flexible" indicates the additional inclusion of low molecular weight multi-functional reactants to the foam system previously described, (or by other methods well known in the art) to produce foams with relatively high crosslink densities.
Even the evaluation of fire retardance is a vexed question, and innumerable test methods have been developed in attempts to ascertain the behaviour of cellular materials in a fire. It has now become generally recognized that small scale laboratory tests are of limited value and are useful mainly only for process control purposes. A useful way to predict behaviour in an actual fire situation is with a full scale and complete seat assembly with a correspondingly large heat source. Such tests may be made under specified conditions or if not carried out in a conditioned environment the tests may be conducted with different materials at the same time to compare the behaviour of these different materials. The latter tests have in fact been conducted. The heat source consisted of 125 gm of newspaper crumpled into balls and placed in one double sheet of newspaper made up into a box. This total fire load was placed on the foam cushion in contact with the "squab". Two 15".times.15".times.4" pieces of foam, one to act as the "cushion", the other as the squab, were placed on a public transport type seat totally made from metal, as they would be when part of a normal seat construction. That is, the squab was placed against the back of the seat which was of sheet metal, at an angle, and the cushion was placed on the horizontal sheet metal seat in front of and in contact with the squab. The metal seat was enclosed in a hood to prevent draughts which might adversely affect some trials and not others, Observations were made and times recorded at the height of the burning ignition source, at the height of involvement of the foam, and after the finish of the trial. for ease of later reference, such tests are called `the Transport Test`.
As previously suggested it has been difficult in the past to produce a flexible polyurethane which would behave well in the abovementioned tests. ICI state, for instance, in their Technical Service Note No. TS/B/2119/1 Table 16, Page 12 that the cited foams when tested according to ASTM D 1692-59T, method 9, Appendix 1, could only be rated "self-extinguishing" and not "non-burning".
In the formulations quoted by ICI on Page 13 of the abovementioned publication, 7.5 parts of antimony trioxide and 15 parts of a chlorinated paraffin namely Cereclor 56L or 65L, suggest an optimum level (or ceilings) of these flame retardants it is possible to include in the formulation. The polyether employed in all these formulations is Daltocel T56, a polyol which contains in the main secondary hydroxyl end groups.
The prior art discloses various means for imparting flame-retardant properties to polyurethane foams. For example, U.S. Pat. Nos. 3,075,927 and 3,075,928 to Union Carbide Corporation disclose polyurethane foams in which flame-retardance is imparted by a combination of antimony trioxide and a vinyl chloride resin.
In British Pat. No. 1,453,178 to M. & T. Chemicals Inc. the flame-retardance is provided by a composition consisting essentially of antimony trioxide, a halogen-containing polymer such as a vinyl chloride resin, and barium carbonate.
British Pat. No. 1,256,672 to The General Tire & Rubber Company describes polyurethane foams in which flame-retardance is imparted by a combination of a solid halogen-containing polymeric resin such as a vinyl chloride resin, zinc oxide and antimony oxide.
U.S. Pat. No. 3,876,571, again to General Tire, is similar to British Pat. No. 1,256,672, and teaches a chlorinated paraffin replacing up to as much as 80% by weight of the solid halogen-containing polymeric resin in this polyvinyl chloride, zinc oxide ad antimony oxide based flame-retardant combination.
U.S. Pat. No. 3,884,849, once again to General Tire, is similar to U.S. Pat. No. 3,876,571, except that there is also present in the combination a zinc salt of an organic monocarboxylic acid or of an organic mono dithiocarbamic acid and, moreover, the chlorinated paraffin is optional as a replacement for part of the solid halogen-containing polymeric resin. U.S. Pat. No. 3,931,062, a yet further grant to General Tire, is similar to U.S. Pat. No. 3,884,849, except that instead of the zinc salt there is employed an oxide, hydroxide or basic salt of certain Group 2a metals, namely magnesium, calcium, strontium or barium.
U.S. Pat. No. 3,799,897 to Toyo Rubber Chemical Industrial Corporation reveals a flame-proof composition of antimony oxide and chlorinated paraffin for polyurethane foams and to this extent differs from say U.S. Pat. Nos. 3,075,927 and 3,075,928 where a vinyl chloride resin is employed in accompaniment with the antimony oxide.
British Pat. No. 1,456,805 to The Upjohn Company discloses flame-retardant flexible polyurethane foams including a combination of antimony oxide, a polyhalogenated aromatic compound and alumina trihydrate.
British Pat. No. 1,368,931 to General Tire incorporates into the foam composition a combination of a solid halogen-containing polymeric resin such as, for example, a vinyl chloride resin, alumina trihydrate and antimony trioxide. Up to 70% by weight of the polymeric resin can be replaced by a chlorinated paraffin. This specification discloses an improvement in the fire retardant effect arising with an increasing concentration of polymeric resin, antimony trioxide and alumina trihydrate (subject to the limits therein specified). However, in this case those skilled in the art would appreciate that the viscosity of the mixture would be such that it would be probable that many conventional machines currently used in commercial production could not be used without modification. The specification teaches that replacement of part of the halogen-containing polymer with a chlorinated paraffin, still gives "useful" foams having sufficient extinguishing properties. However, this qualification is coupled with the warning that when all of the resin is replaced with chlorinated paraffin, the resulting foams exhibit poor cell character, tend to collapse, show poor charring and are not self-extinguishing.
Workers in this area have faced a particular problem for while it has been possible to make some foams with acceptable fire retardant properties, the physical properties of many of these foams are such that the material is only suitable for purposes such as providing insulation, etc. when the material is encapsulated or otherwise contained. Other foams, while having acceptable physical properties, do not have adequate fire retardant properties. Accordingly, it is desirable to produce a polyurethane foam having adequate fire retardant properties and at the same time having the physical properties necessary for applications such as seat cushioning, particularly in public transport vehicles, and for mattresses, particularly in public hospitals.
Notwithstanding the teaching of the prior art it has been surprisingly discovered that these results may be achieved without the need for incorporating a polymeric resin in the foam. A feature of the present invention is the selection of the polyol. More particularly, the polyol must be a diol- or triol-based polyol wherein at least 50% of the hydroxyl end groups are primary hydroxyl end groups.